schorch electric motor rewind 1

[monfils]

We have recently aquired a Schorch 295KW 660v 50Hz electric motor as part of a machinery package. Our plant operates at 440v 60Hz. I have been given many conflicting views as to the best solution, rewinding, or a transformer.
The motor is to drive a primary impactor in a quarry operation. We are unclear as to whether rewinding will enable us to correct the Hzs to the desired 60. We are also unclear as to whether rewinding will effect the performance of the motor.

 

[itsmoked]

faq237-1224
Read that to get up to speed on the subject.

You can certainly use the motor on 60Hz since that is the direction that won't cause you saturation issues.

You can also go the rewind route. Money aside that is a good option.

A main point that needs to be addressed however is the fact that the motor will spin on 60Hz, 20% faster. Most machine loads will go up greatly with this kind of speed change causing issues.

A suggestion: You can use a VFD that allows you to run the motor at its native frequency and when the motor chokes down the road, continue using the VFD to run a 60Hz replacement back at the 50Hz speed.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[petronila]

Hi Monfils,

Check the Name plate connection, if is Y for 660 V-50 Hz then your motor will run fine for 380 V-50 Hz connected in Delta and you don`t need to rewind the motor.

Note: 380 V/50 Hz = 7,6 and 460 V/60 Hz = 7.66

In this case you need to check the mechanical conditions on the load looking for mechanical impact due to the motor will spins fast at 60 Hz.

Regards

Petronila

 

[DickDV]

petronila's suggestion is good but you also may want to change the power train reduction ratio to get the machine speed back to normal. The reduction would be increased by 6/5 and is relatively easy to do with belt or chain drives by changing the sheaves or sprockets. If the motor is direct coupled to a gearbox or something similar, that won't be easy or practical to do.

 

[jraef]

Impactors (assuming horizontal) work mainly on speed rather than raw HP, so be careful about messing with the speed unless you have contact with the original designer or someone who understands how the impactor works. It could very well be that if your crusher was designed for export, the issue has already been dealt with in the drive train ratios and will be fine. If it was designed to be used in a 50Hz system, then you will definitely need to change the ratios so that the impactor bar speed is what it was designed for, otherwise you may drastically alter the throughput performance. 20% extra speed may turn your product into dust rather than smaller rock.

 

[gepman]

There is also the safety issue with any rotating equipment. The centrifugal force is proportional to the rpm squared so a 20% increase in rpm will increase the centrifugal force on the impactor by 44%. Impactors, hammermills, centrifuges, and other heavy rotating machinery usually have an upper design limit for rotational speed. You don't want the impactor to come flying apart.

The primary crushers that I have seen in cement quarries have been vertical and just vibrate a small amount. The secondary impactors that I have seen have been horizontal with large flailing hammers. I wouldn't want to increase the speed of the latter without checking on the maximum design speed.

 

[looper89]

It is unclear to me what exactly you are trying to do.

If you are trying to run equipment that was designed to operate a 50Hz speeds than you need realize the things will rotate faster and gearing etc. may need to be changed.

If you are replacing an existing 60Hz motor and 1.2x the RPM on the 50Hz motor is the RPM of the motor you are replacing, you are good to go.